The present invention relates to method and apparatus for measuring the quantity of air inducted in relation to the speed of an internal combustion engine.
Accurate measurement of air quantity inducted to engine cylinders in relation to the speed of the engine is essential to the control of a mixture of air and fuel at a desired ratio for purposes of reducing the amount of noxious emissions. A variety of fluid sensors of the type in which the frequency of oscillatory movement of a working member is used to represent the fluid flow, have been employed for such purposes in preference to the sensors of the analog type in which the fluid flow is represented in analog value, because of their advantages in manufacturing tolerances and sensor aging over the latter. Since the air quantity varies with engine operations, the digital representation of the fluid sensor would vary typically as 40 times as many as its minimum digital value for a corresponding range of engine operations from idle to full throttle operations. This necessitates the use of a counter having a maximum capacity of more than 11 bits, thereby adding the complexity to the counter with an increased cost.